Historically, psychophysical research has helped to understand the functional significance of physiological findings. This taste psychophysics application aims to compliment and corroborate electrophysiological and molecular biological evidence that indicates there are multiple receptors/transduction mechanisms involved in umami taste. Monosodium glutamate (MSG) is the prototypical umami stimulus in psychophysical experiments; it was recently reported, however, that some individuals may have a specific insensitivity to the umami taste of L-glutamate. The first aim in this application is to identify L-glutamate sensitive and insensitive individuals who will be used as subjects to achieve Aims B and C, which further explore umami taste. A quick, reliable screening tool has been developed to examine a sample population of 240 people for variation in umami taste perception. Second, using a variety of psychophysical (cross-adaptation, mixture interaction, intensity rating) and statistical (ANOVA, cluster and correlation analysis) techniques, in combination with several umami tasting compounds, Aim B assesses psychophysical characteristics of umami taste, specifically, whether there are multiple distinguishable perceptual phenomena, or if umami taste is unitary. Third, some umami compounds inhibit bitterness (both physiologically and psychophysically). By assessing the influence of a variety of umami compounds on bitterness, Aim C will determine if the inhibition of bitterness by umami-tasting stimuli is related to umami taste perception, per se, or to an independent mechanism linking umami-tasting stimuli and bitterness.